1. Field of the Invention
The present invention relates to a multi-pot type disc brake including a plurality of pistons for pushing pads to a disc rotor, and a caliper having a plurality of cylinders juxtaposed for accommodating the pistons.
2. Description of the Related Art
A multi-pot type disc brake includes a plurality of pistons, and a caliper having a plurality of cylinders (or pots) juxtaposed for accommodating the pistons. Generally, the cylinders are formed into such an identical shape that all the clearances between the inner circumferences of the cylinders and the outer circumferences of the pistons are equal. In case the wears of the pads are uneven, all the pistons rub the cylinders simultaneously at a braking time. This creates a problem of an abrupt increase in sliding resistances of the pistons to the cylinders. Thus, at the brake ending time, it is difficult for the pistons to return to the positions before the braking actions so that the pads cannot sufficiently leave the disc rotors at a non-braking time. Another problem is the dragging phenomenon, in which the pads are in sliding contact with the disc rotor at the non-braking time.
In the conventional art, another disc brake is known in JP-A-2005-9612. This disc brake includes a caliper, in which cylinders for accommodating pistons on a rotor rotation-inlet side and cylinders for accommodating pistons on a rotor rotation-outlet side are juxtaposed to each other. The clearance between the cylinder and the piston on the rotor rotation-outlet side is made larger than that on the rotor rotation-inlet side. Even in the case where the caliper is deformed to bulge at the braking time, the pistons on the rotor rotation-outlet side are prevented from rubbing the cylinders on the rotor rotation-outlet side. As a result, the difference between the thrusts of the pistons on the rotor rotation-inlet side and the pistons on the rotor rotation-outlet side can be suppressed to reduce the uneven wears of the pads.
Because of the large clearances between the cylinders on the rotor rotation-outlet side and the pistons, however, a problem arises in that the durability of the sealing members for sealing those clearances is degraded. On the other hand, the pistons are usually plated on their surfaces with chromium or nickel for preventing damages. As shown in FIG. 5, therefore, the piston 13 is inclined with respect to the cylinder 12a, and its bottom 13a is liable to come into sliding contact with the inner circumference of the cylinder 12a thereby forming a pit 12a2 in the inner circumference 12a1 of the cylinder 12a. As a result, the pit 12a2 makes if more difficult for the piston 13 to move relative to the cylinder 12a and the piston 13, after the braking ends, to return to the position before the braking actions. This raises another problem of the dragging phenomenon of pads 15 by a disc rotor R.
Thus, there is a need in the art for a disc brake, which is constituted to suppress the development of the uneven wear of the pads without degrading the durability of the seal between the cylinder and the piston and to suppress the dragging phenomenon of the pads by the disc rotor.